【作者】 付艳恕；

【导师】 范宝春； 孙宇新；

【作者基本信息】 南京理工大学 ， 工程力学， 2009， 博士

【摘要】 块体非晶复合材料诸多优异的物理、力学性能,使其在民用及国防领域具有广泛的应用前景。但由于急冷凝固制备手段的冷却速率约束,使得三维尺寸难以形成大尺度块体而限制了实际应用。块体非晶复合材料制备是目前研究的热点,国内、外均开展了广泛而深入的研究,开发了诸多制备方法,使块体尺寸得以有效的扩大。其中爆炸焊接制备是重要的手段,得到了广泛的重视。应用此法制备块体非晶复合材料是典型的冲击动力学问题,以此为中心,本文开展了系列研究。对非晶薄带爆炸焊接制备块体非晶复合进行讨论。基于弹性薄板静载弯曲理论知实验不能采用间隙铺设;又由于表面粗糙度能为焊接提供层间碰撞空间,因而采用叠层铺设,并就薄带组叠层密度与冲击温升内在关系进行分析。再考虑到非晶薄带较高的硬度及温度敏感性,使其复合下限偏高而上限较低,导致复合窗口狭窄。针对以上困难,提出对非晶薄带进行了涂层;再根据应力波理论,借签损伤力学思想对实验装置进行缺陷设置,以加速反射拉伸波的衰减,从而相应提高焊接上限。另外,对薄带组受爆轰驱动的宏观运动过程进行研究,得到位移、密度及速度时程曲线;根据有限元理论对EPIC-2D程序进行相应的修改,以完成对爆炸焊接过程层间碰撞数值模拟,以了解碰撞过程中焊接界面应力、应变情况及碰撞产生的界面温度场。最后对多层薄带爆炸焊接制备非晶复合块体进行实验,将所得块体进行切割测试,并从冲击动力学及晶化动力学两个角度对实验效果进行分析。分析结果表明非晶薄带组爆炸焊接过程中冲击温升不可忽略,通过调节薄带组装填密度可以控制冲击温升。对薄带进行涂层不仅能降低焊接下限,且能改善薄带组受热状况,更有效地保护其亚稳态结构;而实验装置的缺陷设置可以加速反射拉伸波的衰减,保护复合界面不被撕裂,成功提高焊接上限;综合效果表现为扩大焊接窗口。薄带组三条宏观运动曲线均明确体现了冲击加载过程中的惯性及应变率延迟等效应;有限元法模拟得到的应力、应变及温度场云图说明碰撞过程中界面及内部非晶成分能保存完好。样品X射线衍射及DSC测试结果均表明其结构仍呈非晶态,SEM照片反映涂层界面及复合界面结合良好,薄带未因冲击而发生碎裂。认为隔离了爆轰产物直接作用,转移了碰撞应变、应变率及绝热剪切热,使非晶不能发生结构驰豫,又由于复合过程中压力及热效应的瞬态性,避免扩散形核晶化。更多还原

【Abstract】 Metallic glass composite materials have some properties in mechanics and physics better than crystal metals, so it can be widely used in civil and national defense industry as structural material. But because of the rapidly solidified limitation of cooling rates, at present the actual application was restricted by its three dimensions size. At present, preparing bulk metallic glass composite is the research focus, so extensive and further researches have been done at home and abroad, and developed some prepared methods. As a result, bulk metallic glass composites were larger in size. Explosive welding is one of the most important method, people pay more attention on it. This method is a classical impact kinetics method, in this paper, series studies have been developed.The explosive welding of preparing bulk metallic glass composites by amorphous foils is first to be discussed. It can be deduced by theory of elasticity that the experiment can not lay as metal plate with macro clearance between layers. And because its surface roughness can provide acceleration, it can be laid as superposition which is the style that put one upon another without macro clearance. Then the relationship between initial density and impact temperature was analyzed. Second, prosperities of amorphous foils higher surface hardness and temperature sensitivity, they make the explosive welding low limitation higher and upper limitation lower respectively, so window is narrower. Considering difficulties mansion above, it has been done that coated with another metal at amorphous foils to reduce its surface hardness. Besides, based on the theory of stress wave transformation and reflection, we introduced ideas of damage mechanics to set defects on experiment device. These defects can accelerate the attenuation of tension wave, so the strength of tension wave which arrive at welding interface is weaker. And the upper limit was increased. In researches of impact response, the motion differential equation of integral compressible by detonation products was given out, and gained its numerical results which were used to draw curves of displacement, density and velocity. Besides, based on finite elements theory, the EPIC-2D computer program was modified to make sure it suitable for simulating impaction between layers during explosive welding. By its result, we can analysis stress, strain and temperature field of welding interfaces. Lastly, bulks metallic glass composite materials were prepared by multilayer explosive welding. Samples were cut to test, and results were explained by impact dynamics and crystallization kinetics. Results show out that the impact temperature of multilayer amorphous foils explosive welding can not be neglected, and it can be controlled by adjustment of density of amorphous foils. The coated metal not only decreased its low limitation, but also improved the heat situation of amorphous matrix. These effects are beneficial to protect amorphous as metastable state. Defects on experiment device can accelerate the attenuation of tension wave, so can protect welding interfaces from cracks and increased upper limitation. Lower low limitation and higher upper limitation make the welding window wider. In curves of impact response, characters of inertial and strain rate effect in dynamic mechanics were reflected, and by cloud pictures of stress, strain and temperature field of welding interfaces, it can be concluded that the interfaces and matrix can be preserved well. Both of curves of XRD and DSC confirmed that the amorphous foils matrixes metastable state was maintained in bulk. SEM images reflected conditions of welding interfaces and coating interfaces. It can be concluded by images information that foils didn’t crack and interfaces combined each other very well. We believe that strain, strain rate and adiabatic shear energy were all concentrated on coated metal, and detonation products were isolated, these make sure amorphous matrixes didn’t transform to liquid, so can not occur structural relaxation. And because of characters of transient physics in explosive welding, temperature and pressure were attenuated in few minutes, the time isn’t enough to diffuse for atom, so can not form nucleus and crystallize.更多还原